1. Field of the Invention
The present invention relates to a control device for a vehicular drive system, and more particularly to techniques for permitting an adequate shifting control of a vehicular drive system which includes a differential mechanism operable functioning as an electrically controlled differential device having a differential function, and an automatic transmission constituting a part of a power transmitting path between the differential mechanism and drive wheels of a vehicle.
2. Discussion of Related Art
There is known a vehicular drive system including a differential mechanism operable to distribute an output of an engine to a first electric motor and an output shaft, and a second electric motor disposed between an output shaft of the differential mechanism and the drive wheels. Examples of this type of vehicular drive system include a drive system for a hybrid vehicle as disclosed in Patent Document 1. In this hybrid vehicle drive systems, the differential mechanism is constituted by a planetary gear set, for example, and a major portion of a drive force of the engine is mechanically transmitted to the drive wheels through a differential function of the differential mechanism, while the remaining portion of the drive force of the engine is electrically transmitted to the second electric motor through an electric path between the first electric motor and the second electric motor. Thus, the differential mechanism can function as a transmission the speed ratio of which is electrically variable, for instance, as an electrically controlled continuously variable transmission. The vehicular drive system is controlled by a control device such that the engine is operated with the highest operating efficiency, to drive the vehicle with improved fuel economy. The vehicular drive system of Patent Document 1 further includes a step-variable automatic transmission disposed in the power transmitting path between the output shaft of the differential mechanism and the drive wheels, so that the second electric motor can be small-sized.                [Patent Document 1] JP-2000-2327A        [Patent Document 2] JP-2000-346187A        
In a vehicular drive system including an automatic transmission provided with a fluid-operated power transmitting device such as a torque converter, on the other hand, the engine speed is generally raised owing to a slipping motion within the torque converter, and the shifting of the automatic transmission is controlled such that the engine speed coincides with a speed of synchronization after completion of a shift-down action of the automatic transmission.
However, the vehicular drive system as disclosed in Patent Document 1 wherein the fluid-operated power transmitting device such as a torque converter is not provided, suffers from a possibility of inadequate shifting control due to inadequate control of the engine speed caused by inadequate timings of shifting control of the differential mechanism and shifting control of the automatic transmission.